Modify ovine prolactin by chemical and enzymatic means in order to determine if there are critical amino acid residues involved in binding of the hormone to membranes, activation of adenylcylase, and stimulation of a-lactalbumin formation. Prolactin will also be selectively degraded into fragments which have linear and/or tertiary structure in order to determine if unique linear peptides or tertiary structure units are required for various levels of activity. Testing at two levels of activity as membranes and synthesis of a specific product as a-lactalbumin are critical for dissociating possible differences in the structure of prolactin which may relate to binding or to other biological functions.